This invention relates to an improved perforating blade and signature for use in cutting sheet material which is to be folded and joined together.
It has been known in the printing industry of the difficulties in folding paper without creases or wrinkles forming on the inside page of a chopper folded signature. Because of the wide variety of types, sizes, and weights of paper used, the problem faced by the press-person is the selection of a perforating blade that matches the requirement of the paper being used. Some of those problems are gusseting caused by trying to fold multi-web sheets of paper; difficulty in adjusting a variety of blades used with different types of paper, which causes excessive down time; and the inability to bundle the resultant signatures, the folded stacks of papers which are assembled into a book, because the perforations caused by prior blades result in jagged edges which catch on each other. As a result, the modern press person usually has on hand a large collection of a variety of blades carefully selected from trial and error that are selected and utilized depending upon the type of paper, size of book and so forth.
A number of patents have issued in the art for perforating blades. The Michalik patent, U.S. Pat. No. 4,951,967, is representative. This blade comes in three embodiments, each comprised of a pair of blade sections joined together to form a single blade from which teeth have previously been ground in a variety of configurations. The three configurations noted in Michalik are a "U" shape, an "H" shape, and a "Crank" shape. Each of these teeth shapes are formed by teeth with a straight edge from which extends a lateral edge in order to form the above-mentioned shapes. Each of these shapes perforate the paper on both sides of the fold line and are formed with straight edges at 90 degree angles, preferably. This multi-edged, intricate blade formed of two individually ground sections is very expensive to create and operate compared to the blade of the present invention.
In general, prior art blades, including Michalik and others, still fail to solve all of the aforementioned problems and there was still, until the present invention, no single blade that solved all of the aforementioned troubles. In particular, serrated blades known in the art, damage the ties that hold the paper together in between cuts because, in order to operate, they have to cut deeply. As a result, they also damage the opposing perforating rubber which is typically soft so as to enable the serrated blades to penetrate, but which results in the ties being damaged by pushing and spreading the tie within the soft rubber. A harder, opposing, perforating rubber simply does not work with the standard perforating blade. Further, the major problem, simply put, is that when the paper is folded, the ties binding the paper together normally (unless the correct blade for the correct paper is used) will result in wrinkles.
Thus, there is a need in the art for providing a perforating blade and signature that enhances the twisting ability of the ties and that results in ties that do not lose strength during processing and for a single blade that can be used with many different stock weights and so that the resulting perforated signatures are easily bundled without unwanted gussets or wrinkles. It, therefore, is an object of this invention to provide an improved perforating blade and signature for use in the printing industry with a variety of different stock papers and book sizes.